Modified duo-sol refining



Feb. 14, 1956 H C, MYERS MODIFIED DUO-SOL REFINING 3 Sheets-Sheet l Filed April 25, 1952 Feb. 14, 1956 Filed April 25, 1952 H. C. MYERS MODIFIED DUO-SOL. REFINING 5 Sheets-Sheet 2 Feb. 14, 1956 H. MYERS 2,734,848

MODIFIED Duo-SOL REFINING Filed April 25, 1952 5 sheets-sheet 5 l//ecos/W /N/)ex /05 new 0F w/Jxy @AFF/N475 Z Vom/ME l@ JE INVENTOR Unite i States 2,734,848 MODIFIED DU-SOL REFINNG Application April 25, 1952, Serial No. 11 Ciaims. (Cl. 19d-14.2)

The present invention relates to Duo-Sol refining of mineral oil fractions of varying asphalt content and varying response to treatment when the refining operation is being carried out at the maximum rated capacity for the residuum being charged.

With the demand for high quality lucribating oils increasing and the cost of expanding relining facilities at a maximum, but held in check by various real or imposed shortages, it has become necessary to find some means for increasing the output of Duo-Sol units which are operating at rated maximum capacity. It has been found that the output of a Duo-Sol unit operating at maximum rated capacity can be increased to varying degrees dependent upon the character of available stocks and the point of introduction in the Duo-Sol unit of a secondary feed. Before discussing the application of the present invention to the problem it is considered desirable to discuss the physical system involved in a Duo-Sol extraction.

As those skilled in the art know, a Duo-Sol unit employs two solvents which per se are substantially immiscible. However, the solutions formed during the extraction of mineral oil fraction such as a residuum fraction may become of such character that the solutions of undesirable constituents in the solvent therefor become miscible with the solution of desirable constituents in the solvent therefor. This situation can be more readily understood and analyzed by reference to the twomost commonly employed solvents, to wit: propane and Selectof Selecto is a commercially available mixture of cresols and phenol usually containing from about 2()% to about 65% phenol. Selecto dissolves from an oil, dark coloredlow viscosity index constituents and resinous substances which are readily oxidized or carbonized in service.

Propane rejects asphaltic materials from an oil which, if present, would result in a high carbon residue, and low oxidation stability.

Duo-Sol extraction is conducted commercially in a unit which consists of a series of stages through which the propane and Selecto are passed counter-currently to each other in which each stage represents a single treating stage. The primary or sole feed is introduced into an extraction compartment or stage intermediate those used for charging the two solvents.

Referring now to Figure 1 which is a more or less diagrammatic representation of va Duo-Sol unit having 9 stages or cells or compartments. The oil to be treated is chargedto compartment or cell No. 3 which thereby provides twov propane washing stages for the Selecto extract (cells #1 and #2), and seven extraction stages for the propane solution of thecharge oil (cells 3, li, 5, 6,.7, 8 and 9).

The propane is introduced through line 35 to line 26 where it meets. Selecto phasewithdrawn from cell No. Z through line 18, is mixed therewith and charged to cell No. 1. The Selecto is introduced through line 36 to line 34where it meets propane phase withdrawn from cell No. 8 through line 17, is mixed therewith and charged to celllNo. 9.' The oil to be treated is introduced through line 39 to line 28 where it meets propane-phase withdrawn from cell No; 2 through line 11 and Selecto phase withdrawn from cell No'. 4 through line 20, is mixed theret 2,734,848 Patented Feb. 14, 1956 with and charged to cell No. 3. Extract, composed prithe propane has a lower density than the' Selecto there is' a tendency to form an upper lpropane phase and a lower Selects in each Duo-Sol unit cell. When the oil-Selecto-propane ratio is suitable such a separation into a propane phase and a Selecto phase takes place;

The propane phase from cell No. 1 passes through line 1G `to line 27 where it is mixed with Selecto phasewithdrawn from cell No. 3 through line 19. Thisl mixture of propane and Selecta phases is introduced into cell No. 2; where a separation of propane and Selecto phases takes place, the propane phase passing through line 11 to line 2S where it is mixed with the charge stock as already described and the Selectdphase passesY through line 18 to line 25 where it is 'mixed with charge propane as" described.

One of the most important factors in the operation ofv a" Duo-Sol unit is the establishment of'conditionsvsuch as solvent ratio and ratio of each solvent to the volume of oil v treated so that there is a separation of the' two phases, i. e;,

propane phase and Selecto phase, sufliciently rapid in' each stage to permit practical operation; stage No.3 being particularly critical in this respect.

scribed heretofore. The propane phase from cell No. 4I moves through line 13 to line Si) where it meets the Selecto phase moving through line 22 from cell No.

6, is mixed therewith and passes into cell No. 5 for' phase separation. Similarly, the propane phase from cell' No. 5 passes through lines 14 and 31 to cell No. while" Selecto phase from cell No. 7 passes to cell'No'f 6 through lines 23 and Si.

25 and 33 to cell No'. 8.

to solvent recovery stills.

As those skilled in the art know, the determinationof such physical and chemical properties as viscosity, gravity," viscosity-gravity constant, carbon residue and the like of a" chargestock is not sucient to enable even those'who cari be considered'experts in the art 'of -Duo-Solfreining'rto"= determine, a priori, the proper conditions for the treatment of a feed stock to produce a given qualityraflinate: it is necessary with each 'charge stock or feed to'makeiau extensive pilot plant investigation of the various factors,n propane to Selecto ratio, propane and Selecto to oil"A ratio, extraction temperature and the like before 'corn-k mercial treatment of that particular feed can be attempted? However, once that investigation has produced the ani-- swers, those answers can be translated' and transferredA to: commercial operation successfully.

When refining residua having moderate asphalt content,

the effect of varying Selecto and propane ratios,

Selectotooil ratios and propane-to-oil ratios upon thef yields and properties of the Duo-Sol treated oil (r'al nate) is appreciable.v The eiiect of such variations fis' illustrated by the graphs in Figures 2, 3, 4, 5 Aand '6.

The propane phase of cellt No. 7 passes through lines 16 and 33 to cell No. 3 whileY the Selecto phase from cell No. Q'passes through linesf The propane' phase from cell'.v- No. 8` passes through line 17 to line 3ft-whereV it meets'- incoming fresh Selecto, is mixed therewith and passes; into cell No. 9. The propane phase of cell'No.V 9 passesout of the system as a solution of treated oil in propane materials.

4" Selecta Therefore, the relative Veffectiveness of the two solvents on the viscosity of the product depends large-V ly upon the nature and quantity of the material which' must be removed. The viscosity of oils of loW asphalt content is more responsive to changes in Selecto dosage,

TABLE I Selecta Ratio Increased Constant Decreased Propane Ratio Increased Constant Decreased Increased Decreased Increased Constant Decreased aiglercentvol Decreased..- Decreased... Increased.... Decreased... Increased... Increased..- Indcnite. 'Viscosity Index Increased-.. Increased... Decreased... Increased... Decreased... Decreased..- Do. Viscosity Gravity Consten ..-..do.. Decreased..- Decreased... IncreasecL... Decreased.-- Increased..- Increased.... Do. Carbon Residue Decreased.-. -.-..do Indefinitc.-. Decreased..- Increased Indetinite do Increased. Color Improved... Improved-.. .....do Improved... Impaired.. do.... Impa1red..-. Impaired.

21 F.: v dgtgief Decreased... Decreased... do Decreased... Increased do Increased... Increased. 400% 03H5 Indem'te.-..--.-do Decreased... Increased... Decreased..- Increased,... .do Indetlmtc.

In addition to the effect produced by the variation of the variables discussed hereinbefore, the variables, number of extraction stages and extraction temperature also affect the results. Generally, the efficiency of the Dno Sol treatment is increased by an increase in the number of extraction stages. Usually, increasing the extraction temperature has substantially the same directional eifect as increasing the Selecto dosage at a constant propane dosage.

In general, the viscosity index (V. I.) of an oil is improved by the presence of asphaltic material and deteriorated by the presence of aromatic unsaturated bodies. In Duo-Sol refining, aromatic and unsaturated substances are effectively removed by solution in the Selecto while asphaltic substances are rejected by the propane. Therefore, the V. I. and V. G. C. of radinates can be improved either by increasing the Selecto dosage or by decreasing the propane dosage, or by a combination of both. Improvement in V. I. or V. G. C. obtained by increasing the Selecto dosage or by decreasing the propane dosage is accompanied by a decrease in the yield of ranate.

The yield of raflinate is virtually unaffected by increasingthe amounts of both solvents while maintaining the ratio between them constant although the V. I. is decreased somewhat.

The carbon residue of the Duo-Sol treated oil reflects the quantity of asphaltic, resinous and thermally unstable aromatic and unsaturated substances present-in the ralrinate. In Duo-Sol refining the thermally unstable, resinous materials and asphalt are rejected to the Selecto phase and thereby removed from the system while the treated oil remains in the propane phase. As a consequence, the relative effectiveness of the two solvents for improving the carbon residuel of the oil depends upon the type and quantity of carbon-forming materials which must be removed. The carbon residue of oils of low asphalt content is very responsive to change in Sclccto dosage and less affected by alteration in propane dosage. Conversely, the carbon residue of oils of high asphalt content or asphaltic oils which are to be only lightly refined are more responsive to change in propane dosage.

The dark color associated with most residual oils is due largely to the presence of asphaltic and resinous The relative decolorizing etiiciencies of the two Duo-Sol solvents, therefore, depend on the nature and quantity of the dark colored materials present in the oil to be treated. The color of oils of low asphalt content is very responsive to change in Selecto dosage but less affected by alterations in propane dosage. Conversely, the color of oils of high asphaltic content is more responsive to change in propane dosage.

The viscosity can be altered by varying the quantity of asphaltic, resinous and high viscosity substances present in the oil to be treated. The asphaltic materials can be effectively rejected by the propane, while high viscosity and resinous components of the oil can be removed by the while the viscosity of oils of high asphalt content is more responsive to changes in propane dosage.

In view of the foregoing, it is manifest that the vari-' ations in characteristics of the raihnate are dependent to` a considerable degree upon the combination of tempera ture, Selecto dosage, propane dosage and Selccto-topropane ratio, and to a minor extent upon the number of extraction stages. Consequently, it is necessary before going into commercial operation to go into the laboratory and determine the optimum conditions under which a raffinate of given characteristics can be produced from a given charge stock.

It has nov.7 been found that when a refinery Duo-Sol unit is operating at full capacity for a particular charge stock, a secondary feed can be introduced into the Duo- Sol unit, at some point other than the stage, cell or compartment into which the primary feed or the aforesaid charge stock is introduced, in an amount such that the total yield of raffinate from the treatment of the aforesaid charge stock or primary feed and the secondary feed will be increased considerably, without altering substantially the solvent dosages or solvent ratios employed when treating the particular charge stock or primary feed alone. In other words, under a given set of operating conditions when treating a particular Charge stock, excessV refining capacity exists not for the same charge stock butV for a secondary charge stock of suitable characteristics. To achieve this increase in yield in a unit which, with respect to the primary feed, is operating at capacity, the characteristics of the primary feed and the characteristics of the secondary feed must be correlated.

By characteristics as used in this connection is meant the response to treatment and the content of asphaltic material in the mineral oil fraction to be used as secondary feed relative to the same characteristics of the primary feed.

As was mentioned hereinbefore, the physical and chemical characteristics which are usually determined on a feed stock such as carbon residue, gravity, viscosity, etc., are of little assistance in determining whether or not a secondary feed Vwill be compatible with a primary feed. It is necessary to determine, preferably in the laboratory,

the characteristics of the secondary feed either by a` laboratory Duo-Sol treat or by a single solvent refining such as furfural extraction of the'deasphalted secondary feed, whether the secondary feed will complement the primary feed or not. That is to say, when a Duo-Sol unit is treating the greatest volume of primary feed under given conditions from which a rainate of given'quality can be produced, the capacity of the unit for paratlinic ayrsxigsasY relatively; high' asphaltic ccntentcan be. usedjas a .secondf ary feed.` On the other hand, the compositionvof'a primary feed can be such that while the Selecto phase has limited capacity, relatively, for, extracting additional nonparaiiinic materials the propane phase has appreciable excess capacity-relative1y for'holdingparainic materials in solution without disturbing the settling conditions in the unit. Under these conditions, a relatively high parainicoil contentstock low in asphaltic and other nonparainic constituentsissuitable for use as a secondary l feed. Y

Whilefitwould appear to bepoor-inanagement to use more of one or both solvents than is required to achieve.

the particular extraction, the quantities and ratios of theV solvents used, are notsolely dependent upon the amount of asphalt to be rejected nor upon the amountl of non-paralinic,` non-asphaltic;material to be extracted. The first limiting factor is the amount of each solvent required in the cell into which the feed is introduced to obtain a clean separation of :the propane-oil phase from the Selectooil phase Whentreating the particular charge stock. Then the amount .of Yeach solvent must be adjusted to produce the quality of oil required from that particular unit treating that particular andiclosely similar charge stocks. Finally, For example, a particular chargetstockwhen treated with a givenamount .ofpropaneand Selectof to vyield an oil other limitations must be considered.

reduction of the obtained color tothe required color, being beyond the capacity of the clay..iiltering. plant usedl in conjunction with that particular Duo-Sol` unit, it is necessary to obtain the required color by somey other,r means. This problem can be solved by increasing the, amountV of propane used beyondA thatrequiredltoobtain, the required V. I. andother characteristics ofthe oil.. Asa consequence thereof, an increased amount of propane. is required to obtainthe required colorl under thelimitations of clay filtering. capacity. IJHdenthese` circum-V stancesA that DuoSo1'unit hasr excess capacity fora secondary feed which is ofsubstantiallyY the same responsivenessto treatment andvof 10W to moderate asphaltic content. Y

For the purpose of illustrating the application of the` present invention to theV solution of theproblemof. increasing the yield of ratiinateof given` quality'from a. Duo-Sol unit operating at rated` capacity onl a given., residuum, the treatment of a mixed residuumcontaning- 20 vol. per cent Panhandle, 20 vol. percent Oklahoma City, and vol. per cent Apec-Pegasus residuum will bef discussed. As secondary feed stocks Apec-Pegasus resi-Y duum, Pegasus residuum,vLuling-Lytton Springs Vresiduum, Kuwait propane deasphaltedgresiduum, a heavy.- distillate and Ya light distillate aretobeconsidered. v

rThe charge stocks or feeds-had the propertiesgiven in Table II.

TABLE II Properties of raw stocks charged to modified Duo-Sol operations Apco- Luling- Kuwait Mixed 1 Pegasus 398 Stock 83 Stock Charge Stock Pegasus Lytton P. D. 345

Residuum Residuum Residuum Springs Stock Distillatc Distillatc Inspections:-.

Gravity, A. P. I. (Hydrolneter) 19. 1 2 21. 2 16.0 20. 4 27. 3 22.1; Gravity Specific, 60 F. (Pcyn'r.)-. 0. 9408 0 9468 2 0. 9287 0. 9041 0. 9357 0.8963 0. 9286, Pour Point, F 45 100 Flash POut, F. (COC) 540 545 640 550 575 470' 520 Fire Point, F. (COC) 650 670 710 640 650 545 605 K. V. 210 F., Centlstokes... 74.33 76. 62 56. 68 86.34 33. 70 9. 5l 20.03 S.`U. V. 210 F., Seconds 346 356 264 402 158 57. 5 98. 2 Viscosity Gravity Constant Q 210 F. 0.853 0. 861 0. 840 0.877 0. 855 0.824 0. 850- Color, Lovibond, M `Cell 750 750 750 750 175 275 600' Conradson Carbon Residue, Wt.

percent (Ramsbottom) 6.2 8. 7 6 8 9.8 1 6 Sulphur, percent Wt 0.51 0.47 1.41 2 8 0.31 0. 46

l 20% vol. Panhandle, 20% vol. Oklahoma and 60% vol. ApooPegasus residua,

2 Gravity converted from API hydrometer reading.

of required V. I. will produce oil'of the required V. I. at a certain Lovibond color. However, that color being toohigh to meet thespecification for the oil andthe The secondary feeds when treated in apilot plant Duo- 50 So or furfural refining unit gave the yields of raffinate of the characteristics set forth in Table III. TABLE III Yields and properties of Duo-Sol and ful-,tural refined secondary feed stocks Mixed Crude Residuum (Primary Oil) Processing Conditions:

Duo-Sol Extraction 120 F:-

Selecto, Percent Wt Propane, Percent Wt Fui-tural Refining 230 F., Furfural,

Percent Vol Run No Yields, Percent Vo Ou Extraction.-. On Dewaxing Inspections of Dewaxed Raftnate:

Gravity, API

Pour Point, F Flash Point, F. (COC). S.U. Vg@ 210 F 157 Viscosity Index 96 Viscosity Gravity Constant` 0. 817 Color, Lovibond, 54'! Cell 500 Information on the solvent treatment of the various residual and distillate secondary feed stocks employed in modied Duo-Sol refining studies is included in Table III. These data show that Apco-Pegasus residuum, when treated with the same solvent dosages as the mixed residuum, produces a somewhat lower yield oi a higher viscosity index ranate than obtained by retining the mixed residuum. It would be concluded from this comparative information that ApcoPegasus and the mixed residuum possess similar quality and asphalt content. Pegasus residuum, on the other hand, since it produces a much higher yield of a higher viscosity index ranate than the mixed residuum when treated with the same quantities of solvent, would be adjudged of higher quality and lower asphalt content than the mixed residuum. Luling-Lytton Springs residuum, however, is apparently much lower in quality and higher in asphalt content than the mixed residuum since a high selecto dosageA produces a low yield of only a 94 viscosity index product. Therefore, of these three stocks. Pegasus and Apec-Pegasus would be satisfactory secondary feeds for use with the mixed residuum while Lining-Lytton Springs would he considered unsuitable for use with this primary Duo-So charge stock.

Kuwait deasphalted oil and the light and heavy distillate stocks are known to be substantially asphalt-free. On the basis of Duo-Sol operation, the Kuwait oil appears similar in refining response to the Luling-Lytton Springs residuum and thus would be considered as a poor secondary feed stock for modified Duo-Sol operations with primary mixed residuum. The heavy distillate appears much poorer in quality than the Kuwait stock since treatment with a high furfural dosage only produces a low viscosity index product. This oil would also be an unsuitable secondary feed for use with the mixed residuum. The light distillate, however, provides a high yield of a 94/95 viscosity index oil when treated with a moderate furfural dosage and would therefore be considered about the same as or slightly inferior in quality to the Apec-Pegasus residuum as a secondary Duo-Sol feed stock.

From the foregoing, the primary feed (20% Panhandle, 20% Oklahoma City, 60% Apco-Pegasus) residuum and the available secondary feed stocks ca.nbef.classi tied with respect to response to treatment and asphalt content as follows: i

TABLE IV [Maximum Minimum 0] Relative Relative Stock Response Asphalt to Refining Content Pegasus residuum ,L -i- P-O-A-I mixed residuum. Apco-Pegasus mixed residuum. +4- Panhaudle residuum Oklahoma City residuum Lullng-Lytton Springs residuum.- Kuwait residuum Lig t `listillate 0 He Distillati) 0 Kuwait Propane Deasphalted residuurn -r-f- 0 The mixed Apco-Pegasus-Oldahoma City-Panhandle residuum is classed as being of moderate to low asphalt content and of relatively high paratiinicity. From this point of view it would be normal to use relatively -low Selecto and relatively low propane dosages for retining this oil. However, due to 'the additional need for producing products of satisfactory color in actual relinery practice, relatively low Selecto and yrelatively high propane dosages are actually used. This need for more propane than required for asphaltic constituent removal provides unused `solvent capacity which can he utilized in treating a suitably selected secondary feed stock. (In general average Duo-Sol solvent dosages, expressed as weight per cent based upon the primary feed, are oil:

Selecto: propane=l00z300:300 to produce a 95 V. I. oil while on the aforesaid mixed residuum the ratio is l00:175:425 to produce a 96 V. I. oil.)

The hereinbefore enumerated feeds were charged as secondary feeds to a Duo-Sol unit treating the rated capacity of the aforesaid Apco-Pegasus, Oklahoma City- Panhandle mixed residuum in the amounts indicated with the yields and qualities of ranate indicated in Table V.

TABLE V Primary Feed Mixture of Vol. percent Panhandle, 20 Vol. percent Oklahoma City, et) Vol. percent Apec-Pegasus Residuum to #3 Cell P n d Lillm'l'yt- N n A co-Pe asus Residuurn egasus esi uurn on pgs. Secondary Feed c e p g Resduum Run No 1 2 3 4 5 6 7 8 9 10 11 12 lPercent Primary Feed 25 25 15 25 25 l5 2o 30 35 l5 25 Charged to Cell No 3 5 5 3 3 5 2 2 2 2 2 1 l ht* 175 175 175 175 175 175 175 175 175 175 175 175 eilegredieiltwegigh 425 425 425 425 425 350 350 425 425 425 425 425 Yield, Percent Vol-- G8. 7 67. 8 69. 4 68. 7 68. 0 68. 9 71. 2 74. 1 75. 1 74. 6 57.2 68. 0 Ralnate Gravity, A 25.2 24. 9 25.0 24. 5 25. O 24. 24. 5 24. 9 25. 3 24.6 25. 25.0 Gravity Sp. 0. 2030 0. 9047 0 9042 0. 9071 0. 0. 9003 0. 9071 0. 9047 0. 9024 D. 91h25 0. 9024 0. 9042 i5 15 i5 iigiiiligd 1i5f o' o) 545 aso s55 54s 55o 540 55o 555 550 s45 sus 535 Fire Point F (COC) 630 605 620 635 62o 630 640 540 635 635 620 16 Centistokes 577 571 577 622 590 598 (318 53S 599 623 556 549 0 Centistokes.. 33. 43 33.13 33.21 34. 48 $3. 98 34. 10 35. 83 35. 80 3-1;1 19 34. 72 32. 26 32. 09 100 F., Seconds- 2, 656 2, 63S 2, 565 2, 874 2, 767 2, 763 3, 132 2, 948 2, 168 2, 881 2, 569 2, 536 210 F. Seconds.. 157 150 156 162 161 160 173 168 161 163 152 l U5 9o 94 9G 96 95 97 96 Q5 05 95 o. si? o. 820 o. sis o. sez o. sin o. 82u o. ser o. sis o. 81g o. 821 0. 817 o. szo Cell 500 500 450 500 45D 625 750 '4 650 Y 47o 600 350 425 Y 0. 9408 0 942D 0 9420 0. 9420 0. 9416 0. 9420 0. 9425 O. 9379 0. 9375 0. 9371 0. 9438 0. 9453 verag s {i 1 2, 854 3, 580 3, 520 3, 580 3, 295 3, 580 4, O10 3, 590 3, 725 3, 870 3, 295 3, 580 Relative Volume Percent i 125 125 5 12 140 1 13 13 115 125 Yielgaxy Ralnate, B/SD 1, 970 2, 430 2, 485 2, 460 2, 240 2, 465 2, 850 2, 560 2, 795 2, 885 2, 230 2, 430

' h d B ht ReSltad-vh Y lnj t.) f3.1?. e l 100 123 126 125 114 125 125 135 142 147 114 124 SAE, 30 Percent Rel. Products 5 100 124 127 129 117 126 148 139 142 147 111 121 TABLE V---Continued` Primary Feed Mixture of 20 Vol. percent Panhandle, 20 Vol. percent Oklahoma City, 60 -Vol. percent Apco- Pegasusl Resid-` Pegasus Residnum to #3 Cell uum to Cell #3* Pelrasus` Secondaryl Feed Light Drstillate Heavy Drstrllate Propane Deasphalte (stock ses) (stock se) (Kuwait 345)` Y None Rlfg' Run N o 13 14 15 16 17 18 19 20 21 22 23 24 25 Percent Primary Feed 40 25 25 25 15 l5 l5 10 15 `15 15 25 Charged to Cell No 5 5 5 3 5 2 2 2 5 5 2 selecto, Percent Weight* 175 175 175 175 175 175 175 175 175 175 175 Ui 175 175 Propane, Percent Weight* 350 350 425 425 425 ield, Percent Vol Fire Point, F. '(ooo) K. V; 100 F., Oentstokes 313 380 411 434 K. V. 210 F., Centistokes 22.33 25.65 26. 35 27. 34 S.VU. V. 100 F., Seconds 1, 448 1, 799 1, 899 2,095 S. U. V. 210 F., Seconds 108 123. 126 130 V. I 95 95 94V 9 V. G. C. 210 F 0. 823 0. 820 0. 823 0. 822 Color, Lovibond M" Cell 550 525 525' 450 Total Charge:

Average Sp. Gr. 60 F 0. 9276 0. 9315 0.9315 0.9315

Relative Volume Percent 142 126 126 126 Yields:

Waxy Rainate, B/SD 3, 250 2, 770 2, 825 2, 865

Relative Volume percent Finished Bright Stock 166 141 144 146 SAE, 30 percent Rel. Products... 137 125 130 134 25. 6 25. 0 24. 24. 9 24. 24.15 24 8 25 9 25. 5 0. 9007 0. 9042 0. 9059 0. 9047 0. 9047 0. 9071 0.8990 0.9013 v 20 20 15 15 520 540 555 545 540 565 585 615 595 620 62o 625 615 635 670 685 409 533 539 606 564v 585 584 528 612 26. 71 51. 18 30. 97 34. 35 32.` 53. 33. 06 33.36 32. 23 35. 10 1, 890 2, 462 2, 490 2, 800 2, 606l 2, 703 2, 716 2, 438 2, 827-' 147 146 161 153 156 157 152 165 96 94 93 96 95 94 95 97 0. 818 0. 820 0. 822 0. 819 0. 820 0. 822 0. 820 0. 813 0. 814 42 500 375 750 425 325 l 600 325 450 l Tests on small sample for Wax content determination.

2 Based on 2,864 B/SD charged to Duo-Sol unit during one month employing 20/80 percent Pan/Apec residuum,`245percent Selecto, 425 percent propane 119 F. for 104 V. I. product.

Based on blending bright stock with 42.5 second SUS 210 F. Neutral to 63 second SUS 210 F. S. A. E.30 base stock;

4 Color appears high in view of color of runs 24 and 25.

The data presented in Table VI taken in conjunction with the following discussion is explanatory of the present invention which provides a means for increasing the yield of oil of a given or better quality from a Duoincrease in the amount of Selecto used is equivalent toa decrease in the concentration of Selecto and a modiication of the factors controlling separation as well as` the change inthe properties of the treated oil.

TABLE VI [Primary feed-20% Oklahoma City, 60% Apco-Pegasas resdaam] Oil-Selecto- Relative isc it E. S. Run N o. Secondary Feed, Percent P ropanevnxy Color s /SD-ao Pruio?, Ratio O S. P

, Percen t 1-1. 75-4. 25 96 500 3, 760 100 Apec-Pegasus 2 1-1. 75-4. 25 96v 500 4, 650 124 do 25 3 1-1. 75-4. 25 95 450 4, 770 127v 25 5 1-1. 75-4. 25 94 500 4, 860 129 15 6. 1-1. 75-4. 25 96 450". 4, 390 117 25 3 l-l. 75-3. 50 96 625. 4, 720 126` 25 1-1. 75-3. 50 95 750v 5, 575 148 5 25 2 111. 75-4. 25 97 650 5, 210 139 2 1-1. 75-4. 25 96 475 5, 300 142 2 1-1. 75-4. 25 95 600 5, 520 147 15 2 1-1. 75-4. 25` 95 350 4, 190 111 25 2 1-1. 75-4. 25 95 425 4, 570 121 5 1-1. 75-3. 50 95 550 5, 130 137 25 5 1-1. 75-3. 50 95 525 4, 695 125 25 5 1-1. 75-4. 25 94 525 4, 890 130 25 3 1-1. 754. 25 94 450 5, 055 134 15 5 1-1. 75-4. 25 96 420 4, 215 112 15 2 1-1. 7 5-3. 50 94 500 4, 310 115 15 5 1-1. 754. 25 93 375 4, l170 119 10 2 1"1. 75-3. 00 96 750 4, 170 111 15 2 1-1. 75-4. 25 95 425 4, 425 118 15 5 1-1. 7 5-4. 25 94 325 4, 45() 118 15 5 1-1. 75-3. 50 95 600 4, 590 122 1-1, 75-4.' 25 98 325 4, 670 124 Pegasus 25 2 1-1. 754. 25 97 450 6, 100 162 *Primary feed, Pegasus residuum.

Sol unit without increasing the amount of each solvent but employing an amount of each not less than that required to produce phase separation. In the usual operation of a 7 or 9 cell Duo-Sol unit the charge is introduced into the No. 3 cell; the phase separation conditions in this cell are controlling of the phase separation conditions of the unit. In the No. 3 or feed cell the bulk of the parailinic components of the charge are separated from the non-paraffnic and asphaltic componentsthereof. In order to achieve phase separation, a minimum quantity of Selecta is necessary. Consequently, an. increase in. the amount of charge fed to the No. 3 cell without an Referring nowl to the data presented in Table VI, run No. l yielded data onfthe solvent ratios necessary to produce a 96 V. I. oilhavinga 500'color. The oil- Selectopropane ratio' was l:1.75:4.25. To those skilled in the art it is-manifest that this operation involved the use of an unusually high proportion of propane to produce a light color product. Thus, in accordance with the principlesfof the present invention there is available excess propane `capacity anda secondary feed of moderate orlowfasphalt content can beg-used. Upon referring to the data presented in Table IV\, it.is,-man-, ifest that Pegasus residuum is the most desirable stock :apagada` handle-Oklahoma City-Apco-Pegasus mixed residuum it is the most responsive to treatment and has a low asphaltk content but Apco-Pegasus residuum of moderate asphalt content can also be employed. From the knowledge and experience gained in the Duo-Sol treatment of the primary feed and the rating of the secondary feed with respect to response to treatment and asphalt content it is determined that under steady operating conditions with the P-O-AP mixed residuum as a primary feed, Pegasus or Apco-Pegasus residua can be added to the No. 2 cell Without increasing the amount of either solvent. The amount of secondary feed which can be introduced into the system can only be determined by investigation.

It will be noted that an amount of Pegasus residuum equivalent to 30% by volume or an amount of Apco- Pegasus residuum equivalent to 25% by volume can be introduced into the No. 2 cell with an increase in yield without adversely affecting either the V. I. or the color of the oil produced. However, if the same quantity of Apec-Pegasus residuum is introduced into the No. 3 cell the V. I. is reduced although the color remains satisfactory. (Run No. 3.) On the other hand, if the same quantity (25%) of Apec-Pegasus residuum is introduced into cell No. 5 rather than cell No. 3, the V. I. of the oil produced is unacceptable although the color is satisfactory. (Run No. 4.) While the secondary feed (Apec-Pegasus residuum) can be added in amounts up to 25% of the primary feed in cell No. 2 and cannot be added in that ratio to either cell No. 3 or cell No. 5 without deterioration of the oil obtained, a smaller quantity, i. e., of the primary feed can be introduced into cell No. 5 without adversely affecting the quality of the oil. Similar effects can be obtained by charging the Pegasus residuum to the various compartments.

When the severity of the treatment is increased, 'as for example by reducing the quantity of propane employed which is the equivalent of increasing the concentration of Selecto, the V. I. of the oil produced is satisfactory but the color is unsatisfactory. (Run No. 6.) Nor will the addition of secondary feed (Apro-Pegasus residuum) in a quantity equivalent to of the primary feed into cell No. 3 and 15% of the primary feed into cell No. 5 for a total of 40% of the primary feed produce a satisfactory oil since the V. I. is unacceptable and the color is too high to be handled by the subsequent decolorizing unit. Since the limiting factor for this Duo-So plant handling Panhandle-Oklahoma City- Apco-Pegasus mixed residuum is the capacity of the clay decolorizing unit, the data presented in Table VI for runs Numbers 2, 3, 4, 5, 6 and 7 teach that for this combination of primary and secondary feeds, when employing as a secondary feed a stock which is most responsive to treatment and which has a minimum asphalt content relative to the primary feed, the secondary feed must be introduced into cell No. 2 for maximum yield of oil of the required quality Without increasing the quantity of each solvent employed. However, run No. 5 discloses that with respect to the quality of the oil produced, this secondary feed can be introduced into cell No. 5 but only to the extent of about 60% of the amount that can be introduced into cell No. 2.

Thus, the capacity of the Duo-Sol unit under consideration for the primary feed under consideration can be increased in terms of S. A. E.-30 grade oil having a V. I. of 96 from 3760 barrels per stream day to 4650 barrels per stream day, an increase of 24%, by employing Apco- Pegasus residuum as the secondary feed. In other words, without expanding solvent recovery systems or darkening the color of the oil, without any addition to the Duo-Sol unit and with the same total quantity of each solvent the capacity of this Duo-Sol unit has been increased by 24% without any sacrifice of quality of the oil produced.

Referring now to runs Numbers 8, 9 and 10 it will be noted that a different residuum was used as the secondary feed. Pegasus residuum is more responsive toY treatmentY and has slightly less asphalt than Apec-Pegasus residuum. As a consequence, it is not surprising that a greater quantity of Pegasus residuum can be introduced into cell No. 2 than Apec-Pegasus residuum without adverselyk affecting the quality of the oil produced. As a consequence, about 42% more S. A. E.30, 96 V. I. oil can be produced without enlarging the treating equipment by introducing a quantity of Pegasus residuum equivalent to 30% of the primary feed as secondary feed into cell No. 2 of this Duo-Sol unit.

Luling-Lytton Springs residuum is a` stock which is` appreciably less responsive to treatment than either Pegasus or Apco-Pegasus residua, but has about the same asphalt content as Apco-Pegasus Vresiduum andv slightly more asphalt than Pegasus residuum. Consequently LulingLytton Springs residuum cannot be added in as great a quantity as a secondary feed to cell No. 2 as either Apco-Pegasus or Pegasus residuum to produce a 96 V. I. quality oil. at a level of 15% of the primary feed the oil produced has a very satisfactory color but the V. I. is not acceptable. i* It is of interest to consider the potentiality of light and heavy distillate from a different crude as secondary feeds in this operation; runs Numbers 13 through 20 provide a spectrum of results. When this light distillate (substantially devoid of asphalt) is introduced into cell No. 5 in amounts equivalent to 25% t0,40% of the primary feed the oil produced is not satisfactory as to V. I. (94-95) and is of barely acceptable color. However, when introduced into cell No. 5 in a quantity equal to about 15% of the primary feed the oil producedY is satisfactory with respect to V. I. (96) and color (425).v` In contrast, when the heavy distillate is introduced into cell No. 5 ina quantity equal to about 15% of the primary feed the oil produced is not acceptable with respect to V. I. (93) although of satisfactory color` When the severity of the treatment is increased and a quantity of heavy distillate equal to 15% of the primary feed is introduced into cell No. 2 the V. I. is improved although still unsatisfactory when the goal is an oil of 96 V. I. but the color is suciently low that the oil can be treated in the clay filtering facilitiesavailable. When the severity of the treatment isV further increased by a further reduction in the propaneV used, the oil produced is satisfactory from the standpoint of V. I. (96) but the color is unacceptable because of clay filtering limitations.

Considering runsY Numbers 2l through 23 wherein Kuwait propane kdeasphalted residuum Was used as a secondary feed, it will be noted that, at a level of 15%-of the primary feed, introduction of this propane deasphalted residuumY into cell No. 5 yields an oil which is not.satisfactoryfromthe standpoint of V. I. Thus, for use in conjunction with this primary feed this deasphalted oil is not a Vsuitable `secondary feed although this deasphalted oil would be a suitable secondary feed to be used in conjunctionwith a primary feed whose response to treatmentrirsvmore similar to that of this deasphalted oil.

Upon referring to runs Numbers 24 and 25, it will be noted that under the designation, run No. 24, the significant data for the treatment of Pegasus residuum are collected. The yield of 4670 barrels of S. A. E.30 oil per stream day combined with the relatively high V. I. of

98 indicate that Pegasus residuum is more responsive- It Will'be noted (run No. 1l) thatA No. 3 would be changed and a poor phase separation re-v sult.

The data presented in Table VI therefore represent the treatment of two residua which are very responsive to treatment wherein the variable limiting the type and quantity of secondary feed when used with either of the primary feeds is the capacity of the clay filtering plant to decolorize the Duo-Sol raffinate. Because of this limited capacity the propane dosage is high. As a consequence of the high propane dosage, the quantity of Selecto employed to produce satisfactory phase separation in cell No. 3 is more than required to produce the desired refining effect upon the primary feeds. Accordingly, there is an excess of refining capacity. Therefore, a primary feed of substantially the same response to treatment and having a low to moderate asphalt content can be introduced as a secondary feed into the No. 2 cell in relatively large quantities without an increase in the quantity of either propane or Selecto to produce an oil of substantially the same quality as produced when reating the primary feed alone.

The following tabulation ofdata obtained when operating upon a primary stock of diiferent response and a secondary feed of substantially the same response as the primary charge illustrates another phase of the situation. The primary feed was a Kuwait residuum of substantial asphalt content and moderate response to treatment and the secondary feed was a Kuwait propane deasphalted residuum. The primary feed when treated at a l:2.5:3, oil-Selectopropane ratio was charged at the maximum rate for the particular Duo-Sol unit and its auxiliary equipment and the equipment of the sequential operations of that refinery to produce a 98 V. l. oil.

TABLE VII [Primary feed-Kuwait residuurn] Y Run Number Secondary Feed, percent None 50 Cell Number OilSe1eeto-propane, ra l 2. 5:3 1:2. 5 3 V. I 98 0 Color 83 6l S. A. E.-30 B/SD 100 165 Relative S. A. E.30 Production, percent 100 158 feed had substantially the same response to treatmentl but no asphalt. When the two feed stocks were treated simultaneously without increasing the quantity of either F solvent over that employed for refining the primary feed alone, a high grade oil was obtained and the yield of S. A. E.30 oil was increased by 65% without any increase in plant facilities.

Thus, there has been provided hereinbefore two examples of different conditions which can be encountered in Duo-Sol treating and of the solutions thereto with increased yield of the same quality oil Without increasing the amount of either solvent or the total amount of both solvents and without increasing plant facilities. ln other words, the increased yield of oil of required quality is gotten practically at no cost to the refiner.

Accordingly, the present invention is that improvement in Duo-Sol operation which comprises selecting a secondary feed having a response to treatment complementary to that of the primary feed and introducing said secondary feed into cells No. l or No. 2 or No. 4 or No. 5 or No. 6 or No. 7 or No. 8 depending upon (l) excess propane capacity or excess Selecto capacity, (2) response to treatment compared to the primary feed and 14 (3) asphalt content,y and without increasing the quantity. of either solvent over that required for the primary feed or the total quantity of solvent but .with sufiicient of both' solvents to produce a phase separation in the cell into which the primary feed is introduced, treating both primary and secondary. feeds simultaneously to produce an oil of at least equal quality to that of the oil produced from `the primary feedalone under'the same conditions of solvent ratio and treating temperature.

We claim:

l. ln the Bilo-Sol method` of refining mineral oil comprising paraffinicV and non-parafiinic constituents which comprises extracting in a plurality of stagesl an oil comprising paraiinic and non-parafnic constituents with a refining solvent in the presence of an added liquid having greater solvent power forparatlinic constituents of said oil than for non-paraffinic constituentsof said oil, said solvent for parafiinic constituents of Vsaid oil and said reiining .solvent being adapted to form a two liquid phase. solvent system, the improvement which comprises selecting a secondary feed other than the aforseaid oil having a response to treatment complementary to that of Vsaid oil and of no greater asphalt content than said oil and, whilst the iiow rates of saidA added liquid and said refining solvent remain substantially unaltered and whilst continuing to introduce the'aforesaid oil at a maximum rate concomitant with producing in maximum yield a raffinate of required quality, introducing said secondary feed into said Duo-Sol system ata point other than the point of introduction of said oil intermediate the initial stage and the Y final stage dependent upon therrelative response to treatment and asphalt content as previously determined, and. the more responsive said secondary feed is to treatment relative to said oil the nearer the first stage said secondary feed is introduced to produce a maximum yield of oil of required quality.

2. In the art of refining mineral oil in which an oil comprising parafiinic and non-parafnic constituents as a primary feed'is extracted with a. solvent having greater solvent power for non-parafiinic constituents in the presence of an added liquid having greater solvent power for parainic constituents in a counter-current system havingv a plurality of stages, said solvents being adapted to form a two liquid phase solvent system, the improvement which comprises selecting a secondary feed other than said primary feed having a response to treatment complementary to that of a primary feed, whilst introducing said primary feed at a maximum rate concomitant with a maximum yield of a raffinate of required quality, introducing said secondary feed into a cell other than that into which said primary feed is introduced intermediate the initial and final cells of the system dependent upon the response of said secondary feed relative to the response of said primary feed to treatment, and to produce a maximum yield of oil of required quality the more responsive said secondary feed is relative to said primary feed, the nearer the first stage said secondary feed is introduced, and without increasing substantially the amount of either solvent but with an amount of each solvent sufficient to produce phase separation in the cell into which said primary feed is introduced, treating said primary feed and said secondary feed simultaneously to produce a raffinate of substantially the same quality as produced when treating said primary feed.

3. A method of refining mineral oil which comprises establishing a refining system having a plurality of stages, introducing as a primary feed an oil having paraffinic and non-parafiinic constituents into a stage intermediate the initial stage and the final stage of said system, introducing into the initial stage a solvent having greater solvent power for paraflnic than for non-parafiinic constituents of said oil, introducing into the final stage a solvent having greater solvent power for non-paraflinic than for parafiinic constitu'ents of said oil, both of said solvents being adapted to form a two liquid phase solvent system and being introduced in quantities and in a ratio to separate said oil into a ratiinate having a required V. I. and an extract, establishing-equilibrium conditions in said refining system whereby a given yield of oil of required quality is produced, selecting a secondary feed other than said primary feed having a response to treatment complementary to that of said primary feed, introducing said secondary feed into a stage other than that into which said primary feed is introduced intermediate said initial stage and said nal stage, and without increasing substantially the quantity of either solvent and Without reducing the quantity of said primary feed introduced into said refining system substantially simultaneously refining said primary feed and said secondary feed to produce an increased yield of oil of at least s aid required quality.

4. In the method of rening oil to produce a raihnate more parainic than the charge stock and an extract more non-paralfinic than the charge stock which comprises establishing a refining system having a plurality of stages, introducing as a primary feed an oil having paraflinic and non-paraiiinic constituents into a stage intermediate the initial stage and the final stage of said system, introducing into the initial stage of said system a solvent having greater solvent power for said parainic than for said nonparainic constituents of said oil, introducing into said final stage a solvent having greater solvent power for said non-paraiirlic than for said parainic constituents of said oil, said solvents being adapted to form a two liquid phase solvent system, flowing said solvents in counter-current manner through said system in contact with said oil in amounts and in a ratio to refine said oil to produce a maximum yield of a raffinate of required quality, selecting a secondary feed other than said primary feed having a response to treatment complementary to that of said oil, without increasing the amount of either solvent and without reducing the amount of primary feed introduced into said refining system introducing said oil as a primary feed into said stage intermediate said initial and nal stages and introducing said selected secondary feed into a stage other than that into which said primary feed is introduced intermediate said initial and final stages dependent upon the response of said secondary feed to treatment relative to Said primary feed and` in amount suicient to produce an increased yield of oil of at least said required quality and substantially simultaneously treating said primary and secondary feeds to produce an increased yield of oil of at least said required quality.

5. In the method of refining mineral oil which comprises establishing a refining system having a plurality of stages, introducing into the initial stage thereof a first solvent having greater solvent power for paraiiinic than for non-paraiiinic constituents of a mineral oil, introducing into the final stage thereof a second solvent having greater solvent power for non-paratiinic than for paraffinic constituents of a mineral oil, introducing as a primary feed into a stage intermediate said initial and final stages a mineral oil having paraffinic and non-parainic constituents, the ratio of oil to first solvent to second solvent by weight being within the limits 1:1:1 to 1:7:7 and said solvents being adapted to form a two-liquid phase solvent system, flowing said solvents in counter-current manner through said system in contact with said oil in amounts and in a ratio to produce a rahinate of required quality and recovering a rafnate of required quality, the improvement of which comprises selecting a secondary feed having a response to treatment complementary to that of said oil, continuing to introduce at a maximum rate concomitant with a maximum yield of raffinate of said required quality said oil as a primary feed to said stage intermediate said initial and final stages Without increasing the quantity of either solvent, introducing said selected secondary feed into a stage other than that into which said primary feed is introduced intermediate said initial and final stages dependent upon the response of said feed to treatment relative to said primary feed and in amount suicient to increase the yield of oil of at least required` quality, and simultaneously rening said primary feed and said secondary feed to produce an increased yield of' oil of at least required quality. l t t 6. A method of refining mineral oil which comprises establishinga refining system having a plurality of stages, introducing into a stage intermediate the initial stage and the middle stage thereof a charge oil having parafnic and non-paratiinic constituents, into the initial stage thereof propane and into the final stage thereof Selecto saidY Selecto comprising-a mixture of cresols and phenol containing about 20 to about 65 per cent phenol, adjusting the quantities of oil, propane and Selecto to produce a maximum yield of refined oil of required quality from said rening system, determining that under steady conditions of maximum yield of refined oil of required qualityl from said charge oil there is excess of propane refining capacity, introducing a secondary feed having a response to treatment complementary to said charge oil into a stage intermediate the stage into which saidlprimary feed is introduced and the final stage of said refining system, maintaining an oil Selecto propane ratio substantially no greater than that employed when treating said charge oil as the sole feed to said refining system, adjusting the amount of secondary feed to produce an appreciably increased yield of oil of at least required quality, and refining said charge oil and said secondary feed simultaneously to produce an appreciably increased yield of oil of at least required quality. 7. A method of refining mineral oil which comprises establishing a refining system having a plurality of stages, introducing into a stage intermediate the initial stage and the middle stage thereof a charge oil having paraiiinic and non-parainic constituents, into the initial stage thereof propane and into the final stage thereof Selecto" said Selecto comprising a mixture of cresol and phenol containing about 20 to about 65 per cent phenol, adjusting the quantities of oil, Selecto and propane to produce a maximum yield of rened oil of required quality from said refining system, selecting a secondary feed other than said charge oil having a responsek to treatment complementary to that of said charge oil, introducing said selected secondary feed into a stage other than that into which saidv charge oil is introduced intermediate said initial and final stages of said refining system whilst continuing to introduce said charge oil at the same rate and said propane and Selecto at substantially no greater rate. than before introducing said. secondary feed and regulating the stage of introduction and the rate of introduction to produce a rened oil of at least required quality, v and treating said charge oil and secondary feed to producetan appreciable increased yield of rened oil of at least required quality.

8. A method of refining mineral oil which comprises establishing a refining system having a plurality of stages in excess of three, introducing a rst solvent having a greater solvent power for paraflinic than for non-parainic constituents of a hydrocarbon oil into the rst stage of said refining system, introducing a second solventhaving greater solvent power for non-paraffnic than for parainic constituents of hydrocarbon oil into the final stage of said refining system, introducing as a primary feed a hydrocarbon oil having paraffnic and non-paraffinic constituents into a stage intermediate the initial and middle stages of said refining system, regulating the rate of flow of said primary feed, said first solvent and said second solvent to form a two-liquid phase solvent system and to produce a maximum yield of a raflinate of required quality at the maximum rate of ow of said primary feed whereby the capacity of said first solvent to dissolve further amounts of paraffinic constituents is substantially limited, While the capacity of said second solvent to dissolve further quantities of non-paratfmic constituents is in excess of that realtering the rates of flow of said first and second solvents, introducing into said refining system at a point other than that at which said primary feed is introduced and intermediate said initial stage and the stage next after the middle stage and in quantity sufiicient to appreciably increase the yield of rafiinate of at least the required quality a secondary feed comprising a hydrocarbon oil of low paraffinic constituent content and high asphaltic constituent content relative to said primary feed and simultaneously refining said primary feed and said secondary feed to produce a rafiinate of at least required quality in excess of the maximum amount of raffinate obtainable at the maximum rate of flow of said primary feed.

9. In a Duo-Sol refining system having a plurality of stages in excess of three wherein a primary feed is being treated at maximum rate of fiow with a fixed volume of a first solvent having greater solvent power for parafiinic than for non-paraffinic constituents of said primary feed and with a fixed volume of a secondary solvent having greater solvent power for non-parainic than for parafinic constituents of said primary feed and said first and second solvents are introduced in a mutually fixed ratio to produce a raffinate of required quality at maximum yield for said primary feed said Duo-Sol refining system having excess capacity for paraffinic constituents of a secondary feed or excess capacity for non-paraffinic constituents of a secondary feed the improvement which comprises continuing to introduce said primary feed at the aforesaid maximum rate of fiow whilst maintaining the aforesaid fixed rates of flow of said first and second solvents, introducing a secondary feed, other than the aforesaid primary feed, and having a response to treatment complementaryl to that of the aforesaid primary feed into stages other than those into which the aforesaid primary feed and the aforesaid second solvent are introduced dependent upon (l) which solvent capacity is in excess, (2) response to treatment compared to that of the aforesaid primary feed and (3) asphalt content, and withdrawing a raffinate of the aforesaid required quality in substantially increased amount.

l0. A method of refining a mineral oil which comprises establishing a refining system having a plurality of stages in excess of three, introducing into the initial stage of said refining system a first solvent having a greater solvent power for parafiinic than for non-prafiinic constituents of a hydrocarbon oil, introducing into the final stage of said refining system a second solvent having greater solvent power for non-paraffinic than for paraffinic constituents of a hydrocarbon oil, introducing into a stage intermediate the first and the middle stage of said refining system a primary feed comprising a hydrocarbon oil having parafiinic and non-paraiiinic constituents, regulating the fiow of oil of said first solvent and said second solvent to form a two-liquid phase system and to provide maximum flow of said primary feed into said refining system with the production of a maximum quantity of a raiiinate of required quality whereby the capacity of said first solvent to dissolve further amounts of parafiinic constituents is in excess of that required while the capacity of said second solvent to dissolve further amounts of non-paraiiinic constituents is substantially limited, whilst continuing to introduce said primary feed at a maximum rate of flow and without substantially altering the rates of flow of said first and said second solvents, introducing into said refining system at a point intermediate the stage into which said primary feed is introduced and the final stage of said refining system a secondary feed comprising a hydrocarbon oil having a para'inic constituent content high and a non-parafiinic constituent content low relative to the vsaid primary feed in an amount sufficient to produce an apprcciable increase in the yield of raffinate of at least required qualty, and refining said primary feed and said secondary feed simultaneously to produce an appreciably increased yield of raffinate of at least required quality.

11. In the method of refining mineral oil which comprises establishing a refining system having a plurality of stages in excess of three, introducing into the initial stage thereof a first solvent having greater solvent power for paraflinic than for non-paraffinic constituents of mineral oil, introducing into the final stage thereof a second solvent having greater solvent power for non-paraffinic than for paratiinic constituents of a mineral oil, introducing into a stage intermediate said initial and final stages as a primary feed a mineral oil having paraffinic and non-paraffinic constituents, the ratio of oil to-first solvent to-second solvent by weight being within the limits 1:1:1 to 1:7 :7, and said first and second solvents being adapted to form a two-liquid phase solvent system, owing said solvents in counter-current manner through said refining system in contact with said oil in amounts and in a ratio to produce a raffinate of required quality, increasing the rate of flow of said primary feed, said first solvent and said second solvent until a maximum rate of flow of said primary feed into said refining system at which a maximum yield is attained of raffinate of required quality, whilst the rates of flow of said first and second solvents remain substantially unaltered continuing to introduce said primary feed at said maximum rate of flow whilst introducing into a stage other than that into which said primary feed is introduced a secondary feed other than said primary feed and having a response to treatment complementary to that of said primary feed, said secondary feed being introduced into a stage intermediate said initial and final stages dependent upon the response of said feed to treatment relative to said primary feed, said secondary feed being introduced into said refining system in an amount sufiicient to increase appreciably the yield of raffinate of at least required quality, and simultaneously refining said primary feed at maximum rate of flow and said secondary feed to produce an increased yield of raffinate of at least required quality.

References Cited inthe file of this patent UNITED STATES PATENTS 2,041,308 Tuttle May 19, 1936 2,070,385 Tuttle Feb. 9, 1937 2,079,886 Voorhees May 11, 1937 2,139,392 Tijmstra Dec. 6, 1938 2,225,396 Anderson Dec. 17, 1940 2,248,067 Davis July 8, 1941 2,258,279 Caselli et al. Oct. 7, 1941 

1. IN THE "DUO-SOL" METHOD OF REFINING MINERAL OIL COMPRISING PARAFFINIC AND NON-PARAFFINC CONSTITUENTS WHICH COMPRISES EXTRACTING IN A PLURALITY OF STAGES AN OIL COMPRISING PARAFFINIC AND NON-PARAFFINIC CONSTITUENTS WITH A REFINING SOLVENT IN THE PRESENCE OF AN ADDED LIQUID HAVING GREATER SOLVENT POWER FOR PARAFFINIC CONSTITUENTS OF SOLVENT FOR PARAFFINIC CONSTITUENTS OF SAID OIL AND SAID REFINING SOLVENT BEING ADAPTED TO FORM A TWO LIQUID PHASE SOLVENT SYSTEM, THE IMPROVEMENT WHICH COMPRISES SELECTING A SECONDARY FEED OTHER THAN THE AFORESAID OIL HAVING A RESPONSE TO TREATMENT COMPLEMENTARY TO THAT OF SAID OIL AND OF NO GREATER ASPHALT CONTENT THAN SAID OIL AND, WHILST THE FLOW RATES OF SAID ADDED LIQUID AND SAID REFINING SOLVENT REMAIN SUBSTANTIALLY UNALTERED AND WHILST CONTINUING TO INTRODUCE THE AFORESAID OIL AT A MAXIMUM RATE CONCOMITANT WITH PRODUCING IN MAXIMUM YIELD A RAFFINATE OF REQUIRED QUALITY, INTRODUCING SAID SECONDARY FEED INTO SAID "DUO-SOL" SYSTEM AT A POINT OTHER THAN THE POINT OF INTRODUCTION OF SAID OIL INTERMEDIATE THE INITIAL STAGE AND THE FINAL STAGE DEPENDENT UPON THE RELATIVE RESPONSE TO TREATMENT AND ASPHALT CONTENT AS PREVIOUSLY DETERMINED, AND THE MORE RESPONSIVE SAID SECONDARY FEED IS TO TREATMENT RELATIVE TO SAID OIL THE NEARER THE FIRST STAGE SAID SECONDARY FEED IS INTRODUCED TO PRODUCE A MAXIMUM YIELD OF OIL OF REQUIRED QUALITY. 